Immunological Evidence of Latent Tuberculosis Infection among Noncontacts and Contacts with Index Tuberculosis Patients

Abstract Introduction: Detecting latent tuberculosis infection (LTBI) is becoming more important in cases where the risk of disease progression is high and where anti-tuberculosis (TB) treatment is necessary. The aim of this study is to find out the immunological evidence of LTBI in terms of release of interferon-gamma (IFN-γ), using interferon-gamma release assays (IGRAs) in contacts with the index TB case and without contact individuals. Methods: This cross-sectional study was conducted from March 2023 to January 2024. Participants were recruited according to the inclusion and exclusion criteria, and written informed consent was obtained. Two IGRAs, QuantiFERON-TB Gold In-Tube (QFT-GIT) ® and ichroma™ IGRA-TB assay, a lateral flow assay, were performed on blood samples from participants to detect LTBI. Results: Out of 175 participants, immunological evidence of LTBI was observed in 57 (32.5%) on either assay. By QFT-GIT ® assay, positivity rates were observed as 28.8% (13/45), 18.4% (7/38), and 29.3% (27/92) in close contacts, casual contacts, and noncontacts, respectively. On the other hand, 24.5% (11/45), 15.7% (6/38), and 28.2% (26/92) positivity rates were found in the same groups through ichroma™ IGRA-TB assays. However, these differences were statistically nonsignificant. In addition, the level of agreement (76.6%) between these two assays was observed, indicating good agreement (k = 0.504). Conclusions: The study revealed that the positivity of the IGRA test between the contact and noncontact groups is statistically not significant. The study findings suggest that IGRA testing for LTBI could be reliable for the high-risk group rather than general screening.